Abstract: Despite major strides in understanding of the molecular basis of cancer and cancer therapeutics, the complexities of metastatic process remain poorly understood. Especially in colorectal cancer, it has been severely hampered by limited knowledge about the cells that cause the disease to metastasize through the blood stream. Circulating cells of several lineages are thought to participate in angiogenesis, tumor growth and metastasis. Among these, circulating tumor cells (CTCs) shed from the primary and metastatic carcinomas presumably give rise to blood borne metastases, where as circulating endothelial progenitor cells (CEPCs) from adult bone marrow initiating the pre-metastatic niche. Hence the seed (CTCs) and soil (CEPCs) concept. Although current models explain distinct and important aspects of metastasis, no single model can explain the sum of the cellular changes apparent in human cancer progression and metastasis. I will investigate the inextricable relationship between CTCs, and CEPCs, and their roles in carcinogenesis and metastasis. I propose to take a radical, but integrated technology and biology based translational approach using microfluidic engineering tools to identify, and study the biological relevance of these rare cells in peripheral blood. This approach will seek the following (1) Does the levels of CEPCs and CTCs in early and late stages of colon cancer correlate with each other along with tumor volume and clinical course (2) Can dynamic changes in their load during the course of treatment plan can predict the clinical outcome of the therapy (3) Are there any changes to phenotypic and biological characteristics of these cells that distinguish prognostic subtypes (4) What is the effect of CEPCs on CTCs when cocultured and the fundamental biology of interaction (5) Can we expand these cells in vitro to identify the true "metastatic precursors" or "cancer stem cells" and to determine biomarkers of angiogenesis and metastasis as potential therapeutic targets. Public Health Relevance: There may not be a direct medical benefit to individual participants. However, through this research program, I expect to learn more about novel metastatic markers. Using a novel integrated microfluidic technology, the biological significance of circulating cells in carcinogenesis and metastasis will be investigated. The risks of participating in the research project are reasonable to assume in order to possibly improve diagnostic, prognostic and treatment capabilities for the participants and future patients with cancer.